Melbourne student Suhan Rahman, who has urged young Australians to "spill blood" and "let the heads fly and blood flow", has allegedly made a specific threat to an organisation via social media.
Victoria Police are working closely with the organisation and security has been increased at an undisclosed location.
"We are aware of a threatening comment posted to an organisation's Facebook page. This is being investigated," they said in a statement.
Rahman, 23, of Roxburgh Park in Melbourne's north, has travelled to Syria, where he has posted threatening messages and photographs of himself posing with an AK-47 and other Islamic militants.
In a social media post on Thursday, Rahman urged others to "let the heads fly and blood flow".
"Spill blood young aussies. Dont be humiliated especially if u cant b here in sham (Syria)," he wrote.
Rahman has also praised the recent terrorist attacks in Paris: "May allah accept the french brothers who terrorised france. Day by daywe will bring the war home to you."
He has posted pictures of himself with notorious Sydney extremist Mohamed Elomar, who last year posted pictures of himself holding the severed heads of Syrian government soldiers.
Rahman and Elomar were in a part of Syria controlled by the jihadist group Islamic State.
News Corp Australia reported on Friday the Australian Federal Police counter-terrorism squad had spoken to Rahman's family, and was monitoring his activity overseas.
Rahman's father has reportedly said his son had brought shame on the family.
